Method for estimating vehicular running state, vehicular running state estimating device, vehicle control device, and tire wheel

ABSTRACT

The output level of vibration of a portion below the spring of a vehicle detected by a sensor, and its frequency is converted to obtain the frequency spectrum of the vibration level. Next, an operation is carried out on at least two vibration levels, at different frequency bands. The computed value is compared with a master curve showing the frequency spectrum of vibration level stored in vibration level storage to estimate the condition of a road surface so as to estimate the running state of the vehicle. Further, the running state of each tire including air pressure is detected from the vibration level of the portion below the spring to estimate the running state of the vehicle. Thereby, a multi-function sensing system is constructed for estimating the condition of a road surface or the running state of the tire with one sensor.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and apparatus for estimatingthe running state of a vehicle by estimating the condition of a roadsurface or the running state of each tire while running, an apparatusfor controlling a vehicle based on the estimated running state of avehicle, and a tire wheel comprising the above vehicle running stateestimation apparatus and a power generating unit for activating thisapparatus.

2. Description of the Prior Art

In recent years, it has been desired that the relationship between eachtire and the surface of a road which is the most important factor forthe safe running of a vehicle, specifically, the ground contact state ofthe tire typified by a friction coefficient between the tire and thesurface of a road (road surface friction coefficient) or the conditionof a road surface, or the running state of the tire such as thedistortion and air pressure of the tire should be estimated with highaccuracy and fedback to vehicle control. That is, if the above groundcontact state and running state of the tire can be estimated in advance,before the operation of avoiding a risk such as braking or steering istaken, high-level control of an ABS brake will be made possible andfurther improvement of safety will be expected. The driver can carry outdeceleration operation earlier if he is informed of the risk of thecondition of a road surface while running, whereby a reduction in thenumber of accidents can be expected.

To estimate a road surface friction coefficient, there are proposed amethod of estimating a road surface friction coefficient making use ofthe fact that the uniformity level of each tire which is a physicalquantity indicative of a change in the revolution speed of each wheel ischanged by the size of a road surface friction coefficient (JapaneseLaid-open Patent Application No. 2000-55790) and a method of estimatinga road surface friction coefficient making use of the fact that thehorizontal-direction vibration of each tire having a toe angle isdetected by attaching an accelerometer to a lower arm for connecting thefront wheels and the vehicle body and this vibration level is changed bya road surface friction coefficient (Japanese Laid-open PatentApplication No. 6-258196).

However, in the above method of estimating a road surface frictioncoefficient from the uniformity level of the tire, the uniformity isdeteriorated by the formation of a flat spot in the tire and in thecourse of recovery from this, accurate estimation is difficult.

Meanwhile, in the above method of estimating a road surface frictioncoefficient from the horizontal-direction vibration of the front wheelshaving a toe angle, the measurement accuracy is low when the slip angleof the tire is taken completely null or large.

There is also proposed a method of estimating a road surface frictioncoefficient from transmission characteristics between acceleration belowa spring which is acceleration in the vertical direction of each wheeland acceleration above the spring which is acceleration in the verticaldirection of the vehicle body (Japanese Laid-open Patent Application No.11-94661). This method has such an advantage that the road surfacefriction coefficient on a straight road for which almost no steeringaction is carried out can be estimated because steering force is notused for the estimation of a road surface friction coefficient. However,as the road surface friction coefficient is estimated from vibrationtransmission characteristics between two points through a suspensionunit having large buffer characteristics such as a spring or damper, theroad surface friction coefficient is readily affected by the unevensurface of the road. For instance, as vibration under a spring is largeon a rough road such as a road covered with snow, the difference invibration level between vibration above the spring absorbed by asuspension and vibration below the spring becomes large, thereby makingit impossible to estimate a road surface friction coefficientaccurately.

Meanwhile, the internal pressure of the tire is also an important factorfor the running condition of the tire. Stated more specifically, theground contact state of the tire and the running state of the tire areaccurately estimated from the distortion state or vibration level of thetire while rolling and grip performance is improved or riding comfort isimproved by increasing the ground contact area or rigidity of the tireis reduced to reduce the internal pressure of the tire when the gripperformance of the tire is reduced on a wet road or road covered withiced snow or when the vehicle runs on a rough road. Conversely when thevehicle runs at a high speed or a hydroplaning phenomenon occurs, therunning fuel cost must be improved or the recovery of steerability mustbe promoted by increasing the internal pressure of the tire.

However, since a sensor, which is ground contact state detection meansfor measuring the distortion state or vibration level of the tire whilerolling, requires a electric power source, the power must be supplied tothe above sensor. Further, when an apparatus for estimating orcontrolling the condition of a road surface or the running state of thetire based on the output of the above ground contact state detectionmeans and a radio unit for transmitting an output signal from roadsurface condition estimation means or the like to the vehicle body aremounted to the tire, a electric power supply to the above apparatus andradio unit is necessary.

For the power supply to the tire as a rotor, electromotive force istransferred through a slip ring or generated by electromagneticinduction making use of relative movement between vehicle body and thetire may be used. However, the structure of the vehicle body must bechanged for means of supplying power to these, thus boosting costs.

Although it can be said that it is the most realistic method to loadbatteries which are to be exchanged, there remain such problems as thetroublesome exchange and service life of the batteries.

The development of a system which estimates the running state of avehicle such as the condition of a road surface or the running state ofeach tire accurately, supplies information on the running state of thevehicle to the vehicle and the driver and controls the characteristicsof the tire using the above information to provide a more safe or morecomfortable running state has been desired.

It is an object of the present invention which has been made in view ofthe above problems of the prior art to provide a method and apparatusfor estimating the running state of a vehicle such as the condition of aroad surface or the running state of each tire while running accurately,a vehicle control apparatus for improving the safety of a vehicle byfeedback controlling the running state of the vehicle based on theestimated condition of a road surface or the estimated running state ofeach tire, and a tire wheel comprising the above vehicle running stateestimation apparatus and a power generating unit for activating theapparatus.

SUMMARY OF THE INVENTION

To attain the above object, the inventor of the present invention hasconducted various studies and has found that the running state of avehicle such as the condition of a road surface or the running state ofeach tire while running is estimated by detecting the vibration level ofa portion below the spring of a running vehicle or the vibrationtransmission level between at least two points of a portion below thespring of the vehicle, thereby making it possible to estimate therunning state of the vehicle accurately even when the road is rough,which has been difficult with the prior art, or when the slip angle isnull. The present invention has been accomplished based on this finding.

That is, according to a first aspect of the present invention, there isprovided a vehicle running state estimation method comprising the stepsof detecting the vibration level of a portion below the spring of arunning vehicle, and estimating at least one of the condition of a roadsurface on which the vehicle is running and the running state of eachtire based on the above detected vibration level to estimate the runningstate of the vehicle. Generally the portion below the spring of thevehicle means a suspension, hub, brake caliper, wheel, and tire. In thecase of having no spring in the suspension such as hydraulic unit theportion means on the tire side from the unit.

According to a second aspect of the present invention, there is provideda vehicle running state estimation method, wherein the waveform of timechanges in the above vibration level is detected and the condition of aroad surface on which the vehicle is running is estimated from avibration level at a predetermined position of this waveform or for apredetermined time range.

According to a third aspect of the present invention, there is provideda vehicle running state estimation method, wherein the frequency of theabove detected vibration level is analyzed a vibration level at apredetermined frequency band and the condition of a road surface onwhich the vehicle is running is estimated from the above calculatedvibration level.

According to a fourth aspect of the present invention, there is provideda vehicle running state estimation method, wherein the frequency of theabove detected vibration level is analyzed, at least two vibrationlevels at different frequency bands are calculated, an operation iscarried out on the above calculated vibration levels, and the conditionof a road surface on which the vehicle is running is estimated from theoperated value.

According to a fifth aspect of the present invention, there is provideda vehicle running state estimation method, wherein the vibration levelsof at least two points of a portion below the spring of a runningvehicle are detected to calculate the vibration transmission level ofthe portion below the spring of the vehicle, and the condition of a roadsurface on which the vehicle is running is estimated from the abovecalculated vibration transmission level.

According to a sixth aspect of the present invention, there is provideda vehicle running state estimation apparatus comprising:

means of detecting the vibration level of a portion below the spring ofa running vehicle;

means of computing the waveform of time changes in the above vibrationlevel; and

road surface condition estimation means for estimating the condition ofa road surface on which the vehicle is running from a vibration level ata predetermined position of the above waveform or for a predeterminedtime range.

According to a seventh aspect of the present invention, there isprovided a vehicle running state estimation apparatus which furthercomprises means of calculating the vibration level of at least one of atire leading edge portion, tire ground contact portion and tire trailingedge portion of the above waveform.

According to an eighth aspect of the present invention, there isprovided a vehicle running state estimation apparatus comprising:

means of detecting the vibration level of a portion below the spring ofa running vehicle;

means of calculating a vibration level at a predetermined frequency bandby analyzing the frequency of the above detected vibration level; and

road surface condition estimation means for estimating the condition ofa road surface on which the vehicle is running from the above calculatedvibration level.

According to a ninth aspect of the present invention, there is provideda vehicle running state estimation apparatus comprising:

means of detecting the vibration level of a portion below the spring ofa running vehicle; and

road surface condition estimation means for estimating the condition ofa road surface on which the vehicle is running from a value obtained bycarrying out an operation on at least two vibration levels at differentfrequency bands by analyzing the frequency of the above detectedvibration level.

According to a tenth aspect of the present invention, there is provideda vehicle running state estimation apparatus comprising:

means of detecting the vibration levels of at least two points of aportion below the spring of a running vehicle;

means of calculating a vibration transmission level at a predeterminedfrequency band between the at least two of the above vibration detectionpoints; and

road surface condition estimation means for estimating the condition ofa road surface on which the vehicle is running from the above calculatedvibration transmission level.

According to an eleventh aspect of the present invention, there isprovided a vehicle running state estimation apparatus, wherein avibration buffer member is interposed between the above at least twovibration detection points.

According to a twelfth aspect of the present invention, there isprovided a vehicle running state estimation apparatus, wherein therelationship between road surface friction coefficient μ obtained fromthe braking distances of a vehicle under various road conditions atdifferent speeds and the above vibration level at a predeterminedfrequency band, the computed value of vibration level or vibrationtransmission level is obtained previously and the road surface frictioncoefficient μ at the time of running is estimated based on the aboverelationship.

According to a thirteenth aspect of the present invention, there isprovided a vehicle running state estimation apparatus, wherein the abovefrequency band is a band including the frequency of natural vibration ofa tire tread land portion.

According to a fourteenth aspect of the present invention, there isprovided a vehicle running state estimation apparatus, wherein athreshold value is set for the above vibration level and the surface ofa road is estimated to be in a low friction condition when thecalculated vibration level exceeds the above threshold value.

According to a fifteenth aspect of the present invention, there isprovided a vehicle running state estimation apparatus, wherein the abovethreshold value can be changed.

According to a sixteenth aspect of the present invention, there isprovided a vehicle running state estimation apparatus which furthercomprises vehicle speed detection means to estimate the condition of aroad surface based on vehicle speed.

According to a seventeenth aspect of the present invention, there isprovided a vehicle running state estimation apparatus comprising thevehicle running state estimation apparatus of any one of claims 6 to 16,means of judging the slipperiness of a road surface based on thecondition of the road surface estimated by the road surface conditionestimation means of the vehicle running state estimation apparatus andwarning means for giving a warning when it is judged that the conditionof the road surface is slippery.

According to an eighteenth aspect of the present invention, there isprovided a vehicle running state estimation apparatus which furthercomprises vehicle speed detection means to change decision on theslipperiness of a road surface and warning level based on vehicle speed.

According to a nineteenth aspect of the present invention, there isprovided a vehicle running state estimation apparatus comprising:

means of detecting the vibration level of a portion below the spring ofa running vehicle;

means of estimating the air pressure of each tire by calculating thefrequency of natural vibration of the tire from a vibration level at afrequency band of 200 Hz or less of the above detected vibration level;and

tire running state estimation means for estimating the condition of eachtire while running from the above estimated air pressure of the tire.

According to a twentieth aspect of the present invention, there isprovided a vehicle running state estimation apparatus which furthercomprises tire pressure monitoring means for monitoring the pressure ofeach tire while running using the above estimated air pressure of thetire.

According to a twenty-first aspect of the present invention, there isprovided a vehicle running state estimation apparatus which furthercomprises warning means for warning a passenger of a reduction in thepressure of the tire when the air pressure monitored by the above tirepressure monitoring means falls below a predetermined value.

According to a twenty-second aspect of the present invention, there isprovided a vehicle running state estimation apparatus comprising:

means of detecting the vibration level of a portion below the spring ofa running vehicle;

tire revolution speed detection means;

tire running state estimation means for estimating the state of eachtire while running by calculating the average value of vibration levelchanging by the revolution speed of the tire at a frequency band of 100Hz or less of the above detected vibration level; and

tire trouble detection means for judging that the tire is abnormal whenthe above calculated average value of vibration level exceeds a presetreference value.

According to a twenty-third aspect of the present invention, there isprovided a vehicle running state estimation apparatus, wherein the abovereference value is set to a range of 1.2 to 5 times the vibration levelat a reference decision frequency Fn when the vehicle runs at apredetermined speed V while the tire is not abnormal:

reference decision frequency Fn=n×V/(2πr) wherein r is the rollingradius of the tire, and n is 1, 2, 3, . . . .

According to a twenty-fourth aspect of the present invention, there isprovided a vehicle running state estimation apparatus, wherein the abovereference value can be changed.

According to a twenty-fifth aspect of the present invention, there isprovided a vehicle running state estimation apparatus which furthercomprises a transmitter for transmitting the output of the abovevibration detection means for calculating a time change in vibrationlevel or a vibration level at a predetermined frequency band.

According to a twenty-sixth aspect of the present invention, there isprovided a vehicle running state estimation apparatus further comprisinga electric power generating unit which is mounted to a tire wheel,generates power by the rolling of each tire and supplies power fordriving the above vibration detection means or power for amplifying theoutput of the above vibration detection means.

According to a twenty-seventh aspect of the present invention, there isprovided a vehicle control apparatus comprising vehicle control meansfor controlling the running state of a vehicle based on the condition ofa road surface estimated by the vehicle running state estimationapparatus of any one of claims 6 to 26 and/or the running state of eachtire.

According to a twenty-eighth aspect of the present invention, there isprovided a vehicle control apparatus which comprises vehicle speeddetection means to control the running state of a vehicle based onvehicle speed.

According to a twenty-ninth aspect of the present invention, there isprovided a vehicle control apparatus for comprising means forcontrolling the locked state of each wheel such as ABS to control therunning state of a vehicle.

According to a thirtieth aspect of the present invention, there isprovided a vehicle control apparatus comprising means for controllingthe attitude of a vehicle to control the brake unit of each wheelindependently so as to control the running state of a vehicle.

According to a thirty-first aspect of the present invention, there isprovided a vehicle control apparatus comprising means for controllingthe air pressure of each tire to control the running state of a vehicle.

According to a thirty-second aspect of the present invention, there isprovided a vehicle control apparatus comprising means for controllingthe idling state of each wheel by controlling a brake unit or enginespeed.

According to a thirty-third aspect of the present invention, there isprovided a vehicle control apparatus comprising means for changing theinter-vehicle distance set value of an automatic driving system based onthe above estimated condition of a road surface so as to set anappropriate inter-vehicle distance.

According to a thirty-fourth aspect of the present invention, there isprovided a tire wheel comprising the vehicle running state estimationapparatus as set forth in any one of claims 6 to 26 and a electric powergenerating unit for generating power by the rolling of each tire andsupplying power to the above vehicle running state estimation apparatus.Therefore, as the running state of the vehicle can be estimated for along time without changing the structure of the vehicle body, therunning state of the vehicle can be controlled stably.

According to a thirty-fifth aspect of the present invention, there isprovided a tire wheel, wherein the above vehicle running stateestimation apparatus is mounted to the tire wheel.

According to a thirty-sixth aspect of the present invention, there isprovided a tire wheel, wherein the power generating unit comprises arotor magnetized and rotated by the rolling of each tire, a stator madefrom a high magnetic permeability material and adjacent to the rotor anda power generating coil installed within a magnetic circuit includingthe rotor and the stator. Therefore, power supply to the above vehiclerunning state estimation apparatus is made possible semi-permanently andits functions can be retained for a long time.

According to a thirty-seventh aspect of the present invention, there isprovided a tire wheel, wherein the power generating unit comprises meansof accumulating electromotive force generated in the above powergenerating coil. Therefore, stable power supply is possible regardlessof the running state of the vehicle.

According to a thirty-eighth aspect of the present invention, there isprovided a tire wheel, wherein the rotor is turned by rotating anunbalance weight the gravity center of the rotary cone of which iseccentric to a rotary shaft by the rolling of each tire indirectly orthrough power transmission means.

According to a thirty-ninth aspect of the present invention, there isprovided a tire wheel, wherein an air stream generated by the rolling ofeach tire is introduced into the above power generating unit and theabove rotor is turned by the above introduced air stream.

The other objects, features and advantages of the present invention willbecome apparent from the following description when taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the constitution of a vehicle running stateestimation apparatus according to Embodiment 1 of the present invention;

FIGS. 2( a), 2(b) and 2(c) are diagrams showing the installationlocations of vibration sensors according to Embodiment 1 of the presentinvention;

FIG. 3 is a diagram showing time changes in the vibration level of eachtire according to Embodiment 1 of the present invention;

FIGS. 4( a) and 4(b) are diagrams showing vibration level distributionsin the circumferential direction of the tire on a regular road surfaceaccording to Embodiment 1 of the present invention;

FIGS. 5( a) and 5(b) are diagrams showing vibration level distributionsin the circumferential direction of the tire on an iced road accordingto Embodiment 1 of the present invention;

FIG. 6 is a diagram showing the constitution of a vehicle running stateestimation apparatus according to Embodiment 2 of the present invention;

FIGS. 7( a) and 7(b) are diagrams showing the spectra of vibration inthe circumferential direction of the tire according to Embodiment 2 ofthe present invention;

FIG. 8 is a diagram showing the constitution of a vehicle running stateestimation apparatus according to Embodiment 3 of the present invention;

FIG. 9 is a diagram showing the relationship between the computed valueof vibration level and vehicle speed under various road surfaceconditions according to Embodiment 3 of the present invention;

FIG. 10 is a diagram showing the constitution of a vehicle running stateestimation apparatus according to Embodiment 4 of the present invention;

FIG. 11 is a diagram showing the installation locations of vibrationsensors according to Embodiment 4 of the present invention;

FIGS. 12( a) and 12(b) are diagrams showing the vibration spectra ofvibration transmission level according to Embodiment 4 of the presentinvention;

FIG. 13 is a diagram showing another installation location of avibration sensor according to Embodiment 4 of the present invention;

FIG. 14 is a diagram showing the relationship between road surfacefriction coefficient μ and vibration transmission level according ofEmbodiment 4 of the present invention;

FIG. 15 is a diagram showing the constitution of a road slip alarmaccording to Embodiment 5 of the present invention;

FIG. 16 is a diagram showing a warning zone map according to Embodiment5 of the present invention;

FIG. 17 is a diagram showing the constitution of a road slipperinesswarning apparatus according to Embodiment 6 of the present invention;

FIG. 18 is a diagram showing a warning zone map according to Embodiment6 of the present invention;

FIG. 19 is a diagram showing the constitution of a vehicle running stateestimation apparatus according to Embodiment 7 of the present invention;

FIG. 20 is a diagram showing the relationship between the frequency ofnatural vibration and the air pressure of the tire according toEmbodiment 7 of the present invention;

FIG. 21 is a diagram showing the constitution of a vehicle running stateestimation apparatus according to Embodiment 8 of the present invention;

FIG. 22 is a diagram showing a detection example of a tire peel-offtrouble according to Embodiment 8 of the present invention; and

FIG. 23 is a diagram showing the constitution of a vehicle controlapparatus according to Embodiment 9 of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be describedhereinbelow with the reference to the accompanying drawings.

Embodiment 1

FIG. 1 is a block diagram showing the constitution of a vehicle runningstate estimation apparatus 10 according to Embodiment 1 of the presentinvention. In the figure, reference numeral 11 denotes a vibrationsensor installed on the inner surface of a tire tread, 12 vehicle speeddetection means for detecting vehicle speed based on the output pulse ofa revolution sensor 12 a for detecting the speed of a wheel, 13vibration waveform detection means for obtaining the waveform ofvibration by arranging the output levels (vibration levels) of the abovevibration sensor in time sequence, 14 vibration level distributioncomputing means for obtaining the vibration level distribution of a tiretread by computing the vibration levels in a leading edge portion, aground contact portion and a trailing edge portion of the tire using theoutput pulses of the above revolution sensor 12 a, and 15 road surfacecondition estimation means for estimating the condition of a roadsurface which is one of the running states of a vehicle from the abovecomputed vibration level and the detected vehicle speed using thepreviously obtained master curve of vibration level depending on vehiclespeed stored in vibration level storage means 16.

In this Embodiment 1, the vibration sensor 11 for measuring thevibration state of a tire tread is installed on the inner surface 1A ofthe tire tread (to be simply referred to as “tread” hereinafter) asshown in FIG. 2( a) but the installation location of the vibrationsensor 11 is not limited to this. It may be installed on a portion belowthe spring of a vehicle, for example, the outer side of the rim 2A of atire wheel portion 2 or the suspension arm 3A of a suspension portion 3as shown in FIGS. 2( b) and 2(c).

The above master curve of vibration level is drawn by fixing thevibration sensor 11 on the inner surface 1A of the tread 1 of a testvehicle and causing the vehicle to run on road surfaces which differ inroad surface friction coefficient μ at a speed V to actually measure thevibration level of the above tread 1.

A description is subsequently given of the method of estimating thecondition of a road surface.

First, the vibration level of the tread 1 while running is detected bythe vibration sensor 11 installed on the inner surface 1A of the tread1, a vibration waveform formed by arranging the detected vibrationlevels in time sequence is obtained by the vibration waveform detectionmeans 13, and a curve (to be referred to as “vibration leveldistribution” hereinafter) indicative of a vibration level distributionshowing vibration detection positions on the time axis of the abovewaveform as shown in FIG. 3 is drawn by the vibration distributioncomputing means 14. A power value of vibration level was used as thesize of the above vibration level.

Vibration is generated in the leading edge portion (1) before the treadby an impact when the tread 1 contacts the road surface L. In the tread(ground contact portion) (2) where the tread 1 contacts the road surfaceL, as the tread 1 is confined to the road surface L, vibration is rarelygenerated. Thereafter, in the trailing edge portion (3), vibration isgenerated again by releasing the above confinement as soon as the tread1 departs from the road surface L.

The positions of the above leading edge portion (1), ground contactportion (2) and trailing edge portion (3) and the vehicle speed V aredetected by the vehicle speed detection means 12 based on the outputpulse of the revolution sensor 12 a mounted to each unshown wheel.

The vibration level of the above tread 1 depends mainly on the conditionof a road surface on which the vehicle is running and vehicle speed.

FIG. 4( a) is a diagram showing the vibration level distribution of thetread 1 when a test vehicle runs on a regular dry asphalt road at a lowspeed (V=20 km/h) and FIG. 4( b) is a diagram showing the vibrationlevel distribution of the tread 1 when the test vehicle runs at a highspeed (V=90 km/h).

Meanwhile, when the road surface friction coefficient μ is low, which isgenerally considered as dangerous, the vibration level distribution ofthe tread 1 greatly differs from that when the vehicle runs on the abovedry asphalt road. For example, even when the vehicle runs on an icedroad which is considered to have an extremely low road surface frictioncoefficient μ at a low speed (V=20 km/h), as constraint from the groundcontact surface is small, the tread 1 greatly vibrates in the groundcontact portion (2) where vibration is rarely generated as shown in FIG.5( a). When the vehicle runs on a thick water film at a high speed (V=90km/h), a hydroplaning phenomenon occurs and the vibration level of thetread 1 further increases in the ground contact portion (2) and thetread 1 greatly vibrates even in the leading edge portion (1) as shownin FIG. 5( b).

This is because the tread 1 greatly vibrates even in the ground contactportion (2) where vibration is rarely generated as constraint from theground contact surface is small when the road surface frictioncoefficient μ is low or when the tire is floated by the water film.Particularly when a hydroplaning phenomenon occurs, the vibration of thetread 1 occurs at a position before the essential ground contact surfaceby a water film or water stream formed in front of the tire.

In this Embodiment 1, the vehicle comprising the vibration sensor 11mounted on the inner surface 1A of the tread 1 is caused to run on roadswhich differ in road surface friction coefficient μ at a speed V toobtain the vibration level distribution of the tread 1 from thecondition of a road surface and the vehicle speed V as parameters, andthis vibration level distribution is stored in the vibration levelstorage means 16 of the vehicle running state estimation apparatus 10 asa master curve for estimating the condition of a road surface.

Therefore, the vibration level distribution of the tread 1 obtained bythe vibration level distribution computing means 14 and the above mastercurve stored in the above vibration level storage means 16 are comparedwith each other to estimate the condition of a road surface.

Alternatively, the operation of comparing the measured vibrationdistribution curve and the master curve is simplified, a threshold valueis set for one or a plurality of predetermined vibration levels atdetection positions or for a predetermined time range, and the road isestimated as a low-μ road when the above computed vibration levelexceeds the above threshold value. For example, the vibration level ofthe tread 1 in the ground contact portion (2) which satisfiesrequirements for road surface friction coefficient μ and vehicle speedwhich are considered as safe is stored in the vibration level storagemeans 16 as the above threshold value and the computed vibration levelof the tread 1 in the ground contact portion (2) while running iscompared with the above threshold value to estimate whether the road onwhich the vehicle is running is a safe high-μ road or slippery low-μroad. It may estimated whether the road is a high-μ road or low-μ roadfrom the two vibration levels of the leading edge portion (1) and theground contact portion (2).

Alternatively, the ratio (P1:P2:P3) of the power values of vibrationlevel at the positions (1), (2) and (3) under various conditions of aroad surface such as a regular dry road and an iced road is stored foreach speed and compared with the ratio of the power values of vibrationlevel at the positions (1), (2) and (3) in the computed vibration leveldistribution to estimate the condition of a road surface.

Embodiment 2

In the above Embodiment 1, the vibration levels of a portion below thespring of the vehicle measured by the vibration sensor 11 are arrangedin time sequence by the vibration waveform detection means 13 and thevibration level distribution of the tread 1 is obtained by the vibrationlevel distribution computing means 14 to estimate the condition of aroad surface. As shown in FIG. 6, frequency analyzing means 14F forobtaining the frequency spectrum of vibration level obtained byconverting the frequency of the above vibration level and vibrationlevel calculating means 14S for calculating a vibration level at apredetermined frequency band of the obtained frequency spectrum areprovided in place of the above vibration level distribution computingmeans 14, and further road surface condition estimation means 15S forestimating the condition of a road surface by comparing the vibrationlevel calculated by the above vibration level calculating means 14S witha master curve for estimating the condition of a road surface from thefrequency spectrum of vibration level stored in the vibration levelstorage means 16S is provided to estimate the condition of a roadsurface from the vibration level at a predetermined frequency band ofvibration of a portion below the spring of the vehicle.

FIGS. 7( a) and 7(b) show the vibration spectra of the tread 1 when thevehicle ran on a regular dry asphalt road and the road surface frictioncoefficient μ was considered to be extremely low. FIG. 7( a) shows thespectrum of vibration when the vehicle ran on an iced road at a lowspeed (V=20 km/h) and FIG. 7( b) shows the spectrum of vibration whenthe vehicle ran on a water film at a high speed (V=90 km/h).

When the frequency components of the above vibration spectra wereanalyzed, it was found that the vibration level at a frequency of 500 Hzto 2 kHz greatly changes according to the condition of a road surface.This frequency component is identical to the frequency component ofvibration right after the tread 1 departs from the tread on a regularroad surface and estimated to be caused by the shear or the naturalfrequency of distortion of a tread block. Then, it is possible toestimate the condition of a road surface by comparing the vibrationlevel at a frequency of about 1.4 kHz which is the natural frequency ofthe tread block in the above frequency spectrum.

Therefore, the condition of a road surface can be estimated by obtainingthe frequency spectrum of vibration level obtained in the same actualvehicle test as in the above Embodiment 1, storing this vibrationspectrum as a master curve for estimating the condition of a roadsurface, frequency converting the vibration waveform of the tread 1obtained by the vibration waveform detection means 13 by means of thefrequency analyzing means 14F, and comparing the vibration level at apredetermined frequency range obtained by the vibration levelcalculating means 14S with the above master curve stored in thevibration level storage means 16S.

Further, the operation of comparing the measured frequency spectrum withthe master curve of the above frequency spectrum is simplified, avibration level at one or more frequencies close to the frequency ofnatural vibration of the above tread land portion (block) or apredetermined frequency band is calculated, a threshold value is set forthe above vibration level, and it is estimated that the road is a low-μroad when the above vibration level exceeds the above threshold value.

Embodiment 3

In the above Embodiment 2, the condition of a road surface is estimatedfrom the vibration level at a predetermined frequency band calculated bythe vibration level calculating means 14S. As shown in FIG. 8, vibrationlevel computing means 14 for computing at least two vibration levels atdifferent frequency bands of the obtained frequency spectrum is providedin place of the above vibration level calculating means 14 s, and roadsurface condition estimation means 15S for estimating the condition of aroad surface by comparing the computed value of vibration level computedby the above vibration level computing means 14R with a master curve forestimating the condition of a road surface from the frequency spectrumof vibration level stored in the vibration level storage means 16R isprovided to estimate the condition of a road surface.

The above two frequency bands are preferably 300 to 1,000 Hz which ishardly affected by the condition of a road surface and 800 to 5,000 Hzwhich reflects the slipperiness of a road surface in the spectrum ofvibration of a portion below the spring of the vehicle shown in FIGS. 7(a) and 7(b).

The computed value of vibration level is not limited to a value at theabove two frequency bands and a computed value of vibration level atthree or more frequency bands may be computed to estimate the conditionof a road surface.

FIG. 9 shows the results of computing the ratio α of the average valueof vibration level at a frequency band of 300 to 1,000 Hz to the averagevalue of vibration level at a frequency band of 1,000 to 2,000 Hz whenthe vehicle runs on a dry road, wet road and iced road at a vehiclespeed of 15 to 90 km/h.

On the dry road, the above computed value α is about 0.4 with new tiresand worn-away tires regardless of the speed whereas on the wet road, theabove computed value α becomes larger as the vehicle speed increases andworn-away tires than new tires. This is because a hydroplaningphenomenon occurs that the vehicle is in a slippery dangerous state whenthe vehicle runs on the wet road at a high speed with worn-away tires.Meanwhile, on the iced road, the above computed value α is large at 0.8to 1.1 regardless of the vehicle speed.

Thus, by using a computed value from a vibration level at a plurality offrequency bands, the risk of the condition of a road surface can bejudged accurately on a real-time basis regardless of the speed and theabrasion of the tire.

At this point, the reference value which is a threshold value is setusing the relationship between the road surface friction coefficient μand the above computed value α to judge the condition of a road surface(1) as normal when α is equal to or smaller than 0.6, (2) as requiringcare when α is larger than 0.6 and equal to or smaller than 0.9 and (3)as dangerous when α is larger than 0.9 (hydroplaning, snow road or icedroad). Thus, the slipperiness=risk of the road surface on which the canis running can be judged.

EXAMPLE

The following test was conducted using a vehicle with the vehiclerunning state estimation apparatus 10 of the present invention and analarm device which gives an alarm that care must be taken to the driverwhen the above computed value α obtained by the vibration levelcomputing means 14R exceeds 0.6 and an alarm for a danger when the valuea exceeds 0.9.

On a dry road and a wet road having a water depth of 10 mm, the vehicleran with new tires and worn-away tires at a speed of 30 to 90 km/h andon an iced road, the vehicle ran with new tires at a speed of 15 to 60km/h.

As a result, on the wet road, an alarm that care must be taken was givenwhen the vehicle ran at a speed of 60 km/h or more with new tires and ata speed of 45km/h or more with worn-away tires and an alarm for a dangerwas given when the vehicle ran at a speed of 90 km/h or more with newtires and at a speed of 70 km/h or more with worn-away tires. When thevehicle ran with new tires on the iced road, an alarm that care must betaken was given at a speed of 15 km/h or more and an alarm for a dangerwas given at a speed of 30 km/h or more.

Embodiment 4

In the above Embodiments 1 to 3, the method of estimating the conditionof a road surface by detecting the vibration level of a portion belowthe spring of a vehicle while running has been described. It is alsopossible to estimate the condition of a road surface from vibrationtransmission characteristics between two pints of a portion below thespring of the vehicle by detecting the vibration states of the twopoints.

FIG. 10 is a block diagram showing the constitution of a vehicle runningstate estimation apparatus 20 according to Embodiment 4. In the figure,reference symbols 21A and 21B denote first and second vibration sensorsmounted at two different points of a portion below the spring of thevehicle, 12 vehicle speed detecting means comprising a revolution sensor12 a, 23 transmission function computing means for computing a vibrationtransmission function between the above two points from the outputlevels (vibration levels) of the above first and second vibrationsensors 21A and 21B, 24 vibration transmission level computing means forcomputing a vibration level at a predetermined frequency band from thefrequency characteristics of the above transmission function, and 25road surface condition estimating means for receiving the above computedvibration transmission level and a vehicle speed from the above vehiclespeed detecting means 12 and estimating the running state of the vehicleby estimating the condition of a road surface from the above computedvibration transmission level using the previously obtained G-μ mapshowing the relationship between the vibration transmission level foreach vehicle speed and the condition of a road surface, stored in thevibration level storage means 26.

The two points which differ from each other in relative vibrationcharacteristics and are required for obtaining vibration transmissioncharacteristics are preferably two points sandwiching a buffer member.Therefore, in this Embodiment 4, as shown in FIG. 11, the abovevibration sensors 21A and 21 b are mounted on the outer side of the rim2A of a tire wheel portion 2 and on the suspension arm 3A of asuspension 3. The suspension arm 3A on which the above vibration sensor21B is mounted is connected to a hub portion 3C through a proximalrubber bush 3B, whereby the two vibration sensors 21A and 21B arearranged with the buffer member therebetween.

FIGS. 12( a) and 12(b) show the measurement results of vibrationtransmission levels measured by the first and second vibration sensors21A and 21B mounted on the tire wheel portion 2 and the suspensionportion 3 which are portions below the spring of the vehicle,respectively. FIG. 12( a) shows the vibration transmission levels at alow speed (V=20 km/h) and FIG. 12( b) shows the vibration transmissionlevels at a high speed (V=90 km/h).

As obvious from the figures, the vibration transmission levels on aniced road and a water film are extremely higher at a frequency band of500 Hz to 2 kHz than the vibration transmission levels on a regular dryasphalt road. This is because the wheel including the tire is excited bythe vibration within the tread of the tread 1, and vibration between thetire and the wheel and between the suspension and the wheel is easilytransmitted as constraint from the road surface of the tread 1 is smalldue to a low-μ road, resulting in an increase in vibration transmissionlevel at the above frequency band.

Therefore, by monitoring the vibration transmission level at the aboveband, the condition of a road surface can be estimated. Stated morespecifically, the frequency spectra of vibration transmission levels onvarious road surface conditions are previously obtained and stored as amaster curve for estimating the condition of a road surface, a vibrationtransmission function obtained by the transmission function computingmeans 23 is frequency converted, and the obtained frequency spectrum iscompared with the above master curve of the frequency spectra toestimate the condition of a road surface. Alternatively, the vibrationtransmission level at a frequency band of 500 Hz to 2 kHz is calculated,a threshold value is set for the above vibration transmission level andit is estimated that the road is a low-μ road when the above vibrationtransmission level exceeds the above threshold value.

In this Embodiment 4, unlike the prior art described in the aboveJapanese Laid-open Patent Application No. 11-94661, the vibrationtransmission level between two points of the portion below the spring ofthe vehicle is monitored, thereby making it possible to estimate thecondition of a road surface with high accuracy without being influencedby disturbance such as the roughness of the road surface.

As shown in FIG. 13, a metal “float” 4 may be mounted to the tire wheelportion 3 through a buffer member 5 made from an elastic material andthe second vibration sensor 21B may be mounted on this “float” 4 tomeasure vibration transmission characteristics between the above tirewheel portion 3 and the above “float” 4 with the first vibration sensor21A and the above second vibration sensor 21B mounted on the above tirewheel portion 3, respectively.

The buffer member 5 may be a stabilizer or a link bush or may be bondedto a portion below the existing spring. The buffer member is made fromrubber having elastic characteristics (silicon-, olefin- orphenylene-based) or resin (urethane- or Teflon-based).

In the above Embodiments 1 to 4, the regular dry asphalt road and theroad having a low road surface friction coefficient μ have been taken asexamples of the road. The type of the road is not limited to these and aroad is suitably set according to the district and environment where thevehicle is used and the conditions of the road surface may be classifiedinto three or more estimated conditions of the road surface, forexample, (1) high-μ road (μ≧0.6), (2) intermediate-μ road (0.3≦μ<0.6),and (3) low-μ road (μ<0.3).

Since the vibration level of the above Embodiments 1 to 3 and thevibration transmission level of the above Embodiment 4 are changed bytimes variations in the air pressure and temperature of each tire,rubber hardness or the abrasion amount of the tread. If the above mastercurve or the threshold value might be changeable by the above datavalues, the estimation accuracy of the condition of a road surface couldbe further improved.

In the above Embodiments 1 to 4, the condition of a road surface isestimated from the vibration level or vibration transmission level usingthe master curve of vibration waveforms or frequency spectra of variousroad surface conditions. A running test and a braking test are conductedon various road surface conditions, vibration levels or vibrationtransmission levels at those times are measured, and the road surfacefriction coefficient μ between the tire and the test road surface iscalculated from a braking distance on the road surface to draw a mastercurve of vibration waveforms or frequency spectra at each road surfacefriction coefficient μ, thereby making it possible to construct a roadsurface condition estimation apparatus capable of estimating the roadsurface friction coefficient μ using the above master curve from thevibration level or vibration transmission level measured while running.

For example, FIG. 14 plots the road surface friction coefficient μobtained from the braking distance on an iced road, snow road and dryasphalt road on the axis of abscissas and the size of vibrationtransmission level at 50 Hz to 2 kHz of the vibration transmissionfunction described in the above Embodiment 4 (at the time of running ata fixed speed of 20 km/h) on the axis of ordinates. Thus, since theabove road surface friction coefficient μ and the vibration transmissionlevel are closely correlative to each other (R²=0.9983), the roadsurface friction coefficient μ can be estimated from the vibrationtransmission level measured while running with high accuracy.

Embodiment 5

In the above Embodiments 1 to 4, the method of estimating the conditionof a road surface from the vibration level or vibration transmissionlevel of a portion below the spring of the vehicle has been described.When it is estimated from the above vibration level or vibrationtransmission level how slippery the surface of the road is and thecondition of the road surface is estimated to be slippery, it ispossible to warn the driver or passenger of the risk.

FIG. 15 is a diagram showing the constitution of a road slipperinesswarning apparatus 30 according to Embodiment 5. The road slipperinesswarning apparatus 30 comprises map storage means 36 for storing awarning zone map having two warning zones Z1 and Z2 surrounded byvehicle speed V and the size of vibration level shown in FIG. 16 inplace of the vibration level storage means 16 of the above Embodiment 1,road condition judging means 35 for judging where the vibration level ofthe tread 1 obtained by the vibration distribution computing means 14and vehicle speed are positioned in the above warning zone map in placeof the road surface condition estimation means 15 of the aboveEmbodiment 1, and further warning means 37 for warning the driver orpassenger of a risk when the measured vibration level and vehicle speedare in the above warning zone Z1 or Z2.

The road slipperiness warning apparatus 30 of Embodiment 5 activates thewarning means 37, for example, turns on and off an unshown red lamp whenthe vibration level corresponding to the vehicle speed of the tread 1 isin the warning zone Z1 of the first stage and sounds an alarm and turnson and off the above red lamp when the above vibration level is in thewarning zone Z2 of the second stage. Thus, the road slipperiness warningapparatus 30 warns the driver or passenger of the risk of the roadsurface. Since the risk of the condition of the road surface can bethereby informed of the driver while running, the driver can take earlyoperation to decelerate and a reduction in the number of accidents canbe expected.

EXAMPLE

When a test vehicle with the above road slipperiness warning apparatus30 was caused to run on a dry asphalt road or wet road (water poolhaving a depth of 10 mm) by increasing the vehicle speed to 20, 40, 60,80 and 90 km/h gradually, the vibration level of the tread 1 rose as thevehicle speed increased on the regular dry asphalt road (marked with)and the wet road (marked with O) where hydroplaning easily occurs asshown in FIG. 16. Particularly when the road was wet and the vehiclespeed was high, the above vibration level jumped up. On the wet road,the warning of the first stage was given when the vehicle speed became60 km/h and the warning of the second stage was given when the vehiclespeed became 80 km/h or more. Thus, it was confirmed that the object ofthe present invention could be attained.

In the above Embodiment 5, a warning was given by estimating theslipperiness of the road by obtaining the vibration level distributionof a portion below the spring of the vehicle measured by the vibrationsensor like the above Embodiment 1. Like the above Embodiments 2 and 3,the slipperiness of the road may be estimated from the vibration levelat a predetermined frequency band or the value obtained by carrying outan operation on at least two vibration levels at different frequencybands of the frequency spectrum of vibration level obtained by frequencyconverting the above vibration level.

Embodiment 6

In the above Embodiment 5, the risk of the road condition is directlyjudged from the measured vibration level of the portion below the springof the vehicle. The vibration states of two points of the portion belowthe spring of the vehicle are detected and the slipperiness of the roadsurface is estimated from the vibration transmission level between theabove two points to give a warning.

FIG. 17 is a diagram showing the constitution of a road slipperinesswarning apparatus 40 according to Embodiment 6 of the present invention.The road slipperiness warning apparatus 40 comprises map storage means46 for storing a warning zone map having two warning zones K1 and K2surrounded by the vehicle speed V and the vibration transmission level Gshown in FIG. 18 in place of the vibration level storage means 26 of theabove Embodiment 4, road surface condition judging means 45 for judgingwhere the vibration transmission level obtained by the vibrationtransmission level computing means 24 and vehicle speed are located inthe above warning zone map in place of the road surface conditionestimation means 25, and further warning means 47 for warning the driveror passenger of a risk when the above measured vibration transmissionlevel and vehicle speed are in the above warning zone K1 or K2. When thevibration level of the tread and the vehicle speed are in the warningzone K1 of the first stage or the warning zone K2 of the second stage,the warning means 47 is activated to warn the driver or passenger of therisk of the road surface.

EXAMPLE

When a test vehicle with the above road slipperiness warning apparatus40 was caused to run on a dry asphalt road and a frozen road at a fixedspeed of 20, 30 or 40 km/h, a warning of the second stage was given atall the speeds on the frozen road. Thus, it was confirmed that theobject of the present invention could be attained.

In the above Embodiments 5 and 6, the risk of the road surface conditionis directly judged from the measured vibration transmission level. Anestimated road surface condition computing apparatus similar to thevehicle running state estimation apparatuses 10 and 20 of the aboveEmbodiments 1 to 4 may be constructed and a risk may be warned to thedriver or passenger according to the condition of a road surfacecomputed by the estimated road surface condition computing apparatus. Inthis case, it is needless to say that the above road surface conditionsand the warning zones must be set to relate the estimated road surfaceconditions with the set warning zones.

Embodiment 7

In the above Embodiment 2, the method of estimating the condition of aroad surface by calculating a vibration level at a predeterminedfrequency band from the frequency spectrum of the vibration level of aportion below the spring of the vehicle obtained by the frequencyanalyzing means 14F has been described. As shown in FIG. 19, tirenatural vibration calculating means 17A for calculating the frequency ofnatural vibration of each tire from a vibration level at a frequencyband of 200 Hz or less of the detected vibration level, tire airpressure estimation means 17B for estimating the air pressure of eachtire from the calculated frequency of natural vibration of the tire andtire running state estimation means 18 for estimating the running stateof each tire from the estimated air pressure of the tire are provided toestimate the running state of the tire which is one of the runningstates of the vehicle.

FIG. 20 shows the relationship between the frequency of naturalvibration of the tire (Hz) and the air pressure (MPa) of the actualtire. Since the above frequency of natural vibration of the tire and theair pressure of the tire are closely correlative to each other(R²=0.9891), the vibration level of a portion below the spring of thevehicle is detected and frequency analyzed so that the air pressure ofthe tire can be estimated from a vibration level at a frequency band of200 Hz or less of the detected vibration level with high accuracy.

In this embodiment, tire pressure monitoring means 19A for monitoringthe pressure of the tire while running using the above estimated airpressure and tire pressure reduction warning means 19B for warning thepassenger of a reduction in the pressure of the tire when the airpressure monitored by the above tire pressure monitoring means 19A fallsbelow a predetermined value are provided to warn the passenger of areduction in the pressure of the tire. Thereby, the running state of thetire can be estimated and when the pressure of the tire monitored whilerunning falls below a predetermined value, this can be warned to thepassenger, thereby making it possible to improve the safety of thevehicle.

Embodiment 8

In the above Embodiment 7, the air pressure of the tire is estimated bycalculating the frequency of natural vibration of the tire from avibration level at a frequency band of 200 Hz or less of the vibrationlevel of a portion below the spring of the vehicle by means of the tirenatural vibration calculating means 17A and the tire air pressureestimation means 17. As shown in FIG. 21, tire revolution speeddetection means 27, tire running state estimation means 28 forestimating the state of the tire while running by calculating theaverage value of vibration level changing by the revolution speed of thetire at a frequency band of 100 Hz or less of the detected vibrationlevel, tire abnormality detection means 29A for judging that the tire isabnormal when the calculated average value of vibration level exceedsthe preset reference value and tire abnormality warning means 29B forwarning the passenger of the abnormality of the tire based on thedetection result of the above tire abnormality detection means 29A areprovided to estimate the running state of the tire and to judge theabnormality of the tire, thereby making it possible to warn thepassenger of this abnormality.

For example, when part of the tread portion peels off, air in the insideof the tire is excited by the generation of vibration each time the partcontacts the surface of a road. As the initial peel-off trouble occursat one site on the outer surface of the tire, vibration generatedthereby is periodical according to the revolution of the tire. The cycleis about 14 Hz (primary), 28 Hz (secondary) and 42 Hz (tertiary) at aspeed of 100 km/h in the case of a tire for a general passenger vehicle.The above peak generally appears by the ground contact of the tire evenwhile running but when a peel-off trouble occurs at one site on theouter surface of the tire, the above peak level is extremely high,whereby it is estimated that something abnormal occurs in the tire.

Therefore, a vibration level at a frequency band of 100 Hz or less (forexample, 14 Hz, 28 Hz or 42 Hz) of the vibration level of a portionbelow the spring of the vehicle is calculated by the above tire runningstate estimation means 28, it is judged that the tire is abnormalcondition when the average value of the calculated vibration levelexceeds a predetermined reference value, and this information is sent tothe tire abnormality detection means 29A to warn the occurrence ofabnormality in the tire to the passenger.

FIG. 22 is a diagram showing the result of comparison between thevibration level (dB) of a defective tire having a cut at one site on theouter surface between the tire tread and the steel belt and that of anormal tire. Stated more specifically, the above defective tire and thenormal tire were caused to run on an indoor drum at a fixed speed of 100km/h to measure their vibration levels and analyze the frequencies ofthe vibration levels.

As described above, even in the case of the normal tire, peaks appear atfrequencies of about 14 Hz (primary), 28 Hz (secondary), 42 kHz(tertiary), . . . whereas in the case of the defective tire, as shown bya broken line in the figure, the sizes of the peaks are about 20 dBlarger than those of the normal tire. The peaks are much higher than thepeaks of the normal tire at the above frequencies, which are set asreferences for detecting a tire trouble and a tire trouble can bedetected by detecting the vibration level of the portion below thespring of the vehicle.

The above reference value is set to a range of 1.2 to 5 times thevibration level at a reference decision frequency Fn=n×V/(2πr) when thevehicle runs at a predetermined vehicle speed V while no abnormalityoccurs in the tire to detect the above abnormality with high accuracy.In the above equation, r is the rolling radius of the tire and n is anatural number.

The above reference value can be changed by time variations intemperature, the abrasion amount of the tire tread or the deteriorationof the hardness of rubber.

Embodiment 9

FIG. 23 is a diagram showing the constitution of a vehicle controlapparatus 50 according to Embodiment 9. The vehicle control apparatus 50comprises vibration sensors 21A and 21B installed at two differentpoints of a portion below the spring of the vehicle, vehicle detectionmeans 12, transmission function computing means 23 for computing avibration transmission function between the above two points from theoutput levels (vibration levels) of the above vibration sensors 21A and21B, vibration transmission level computing means 24 for computing avibration level at a predetermined frequency band from the frequencycharacteristics of the above transmission function, road surfacecondition estimation means 25 for receiving the above computed vibrationtransmission level and a vehicle speed from the above vehicle speeddetection means 12 and estimating the condition of a road surface usingthe previously obtained G-μ map showing the relationship betweenvibration transmission level for each vehicle speed and the condition ofa road surface stored in the vibration level storage means 26, andvehicle control means 57 for controlling the running state of thevehicle based on the estimated condition of the road surface obtained bythe road surface condition estimation means 25.

The above vehicle control apparatus 57 controls the air pressure of thetire based on the above estimated condition of the road surface andshortens the braking distance on a slippery road. For example, byreducing the air pressure of the tire on a low-μ road such as an icedroad, the braking distance on the low-μ road can be shortened.

That is, when the road is estimated as a low-μ road, the air pressure ofthe tire is automatically or manually reduced by the vehicle controlmeans 57 to increase the ground contact area of the tire, therebyincreasing friction force between the road surface and the tire toshorten the braking distance.

Any tire air pressure automatic control system is acceptable but thesystem comprises a pressure meter, controller, wheel with a pressurecontrol valve, flexible joint hose, spare tank and compressor, forexample.

The vehicle control apparatus 50 may be provided with means of warningthe driver or passenger of a risk according to the condition of the roadsurface as described above to control the running state and give awarning at the same time.

EXAMPLE

A braking test was conducted on a dry asphalt road and an iced roadusing a test vehicle which was loaded with the vehicle control apparatus50 of this Embodiment 9 to control the air pressure of each tire inorder to confirm whether the braking distance could be shortened bycontrolling the air pressure of the tire automatically when the vehiclewas braked on the frozen road. The above vehicle control apparatus 50was provided with a road slipperiness warning apparatus similar to thoseof above Embodiments 5 and 6.

It was first confirmed that when the test vehicle of the presentinvention was caused to enter a frozen road at a fixed speed V of 20km/h, a warning was given and at the same time the air pressure of thetire was automatically reduced from 220 to 160 kPa. This is because whenit is detected that the vehicle enters the frozen road, the computer isprogrammed to give an instruction to reduce the air pressure. Further,when a braking test was conducted on a dry asphalt road and a frozenroad, the braking distance of a vehicle with a conventional controlapparatus was 85% longer than when running on the asphalt road whereasthe braking distance of the test vehicle of the present invention was59% longer. That is, the braking distance of the present invention canbe shortened by about 14% on the asphalt road and about 30% on thefrozen road. It was confirmed from this result that the vehicle can stopsafely even on a frozen road by using the vehicle control apparatus 50of this Embodiment 9.

In the above Embodiment 9, vehicle control means for controlling thelocked state of each wheel and the air pressure of each tire based onthe estimated condition of a road surface is provided to control thebraking distance on a low-μ road. The braking distance on a low-μ roadcan also be shortened by performing the attitude control of a vehicle bycontrolling the brake unit of each wheel independently.

Alternatively, vehicle control means for controlling the attitude of avehicle may be provided to carry out the attitude control of thevehicle, for example, by controlling the brake unit of each wheelindependently based on the estimated condition of a road surface,thereby making it possible to reduce the braking distance on a low-μroad.

Further, vehicle control means for controlling the idling state of eachwheel may be provided to control the idling state of the wheel bycontrolling the brake unit or engine speed based on the estimatedcondition of a road surface, thereby making it possible to reduce thebraking distance on a low-μ road.

Further, in a vehicle with an automatic driving system, vehicle controlmeans for controlling to change the inter-vehicle distance set value maybe provided to change the above inter-vehicle distance set value basedon the estimated condition of a road surface so as to control theinter-vehicle distance to an appropriate value, thereby making itpossible to keep a safe inter-vehicle distance even on a low-μ roadwithout fail.

In the above example, the running state of a vehicle is controlled basedon the condition of a road surface estimated from a vibrationtransmission level like Embodiment 4. Like Embodiments 1 to 3, therunning state of a vehicle may be controlled based on the condition of aroad surface estimated from a vibration level.

Alternatively, the running state of a vehicle may be controlled based onthe running state of each tire estimated by the tire running stateestimation means 18 or 28 shown in Embodiment 6 or 7.

As having been described above, according to the present invention, thevibration level of the portion below the spring of a running vehicle orthe vibration transmission level between at least two points of theportion below the spring of a vehicle is detected to estimate thecondition of a road surface on which the vehicle is running. Therefore,even when the road is rough, which has been difficult with the priorart, or when the slip angle is null, the condition of the road surfacecan be estimated accurately. Using the estimated condition of the roadsurface, the risk of the condition of the road surface is warned to thepassengers or the feedback control of the running state of the vehiclecan be performed, thereby making it possible to greatly improve thesafety of the vehicle.

Further, the condition of a road surface or the air pressure of eachtire is detected from a vibration level at a plurality of frequencybands of the vibration level to detect the condition of the road surfaceor the running state of the tire including the existence of abnormalityof the tire. Therefore, a multi-function sensing system which canaccurately detect the condition of a road surface, tire pressure andfurther the existence of tire abnormality with one sensor, has a simplestructure and many functions and is inexpensive can be constructed.

In the present invention, since an apparatus for estimating the groundcontact condition of each tire or the condition of a road surface and apower generating unit for generating power by the rolling of the tireand supplying power to the above apparatus are mounted to a tire wheelto control the characteristics of each tire based on the estimatedrunning state of the vehicle, the ground contact state of the tire canbe estimated and controlled stably for a long time without changing thestructure of the vehicle body.

Further, since the above power generating unit comprises a rotormagnetized and rotated by the rolling of the tire, a stator made from ahigh magnetic permeability material and adjacent to the rotor, a powergenerating coil installed within a magnetic circuit including the aboverotor and stator and a capacitor for accumulating electromotive forcegenerated in this power generating coil, power supply is made possibleby energy obtained from the rolling of the tire semi-permanently and itsfunctions can be retained stably for a long time.

1. A vehicle running state estimation method comprising: detecting avibration level of a portion below a spring of a running vehicle; andestimating the running state of the vehicle by determining at least oneof a condition of a road surface on which the vehicle is running and arunning state of each tire, wherein said determining is based on thedetected vibration level, and wherein a waveform of time changes in thevibration level is detected and the condition of the road surface onwhich the vehicle is running is estimated from a vibration level at apredetermined position of the waveform or for a predetermined timerange.
 2. A vehicle running state estimation method comprising:detecting a vibration level of a portion below a spring of a runningvehicle; a frequency of the detected vibration level is analyzed tocalculate a vibration level at a predetermined frequency band and acondition of the road surface on which the vehicle is running isestimated by comparing the calculated vibration level with a mastercurve which is a vibration level detected through running on a roadhaving a predetermined condition of a road surface of the runningvehicle.
 3. The vehicle running state estimation method according toclaim 2, wherein the master curve is prepared based on the vibrationlevel detected at the time when the vehicle is running on a surface of aroad with a usual dry asphalt pavement.
 4. A vehicle running stateestimation method comprising; detecting a vibration level of a portionbelow a spring of a running vehicle; and estimating the running state ofthe vehicle by determining a degree of slipperiness of a road surface onwhich the vehicle is running and a running state of each tire, whereinsaid determining is based on the detected vibration level, and whereinthe frequency of the detected vibration level is analyzed, at least twovibration levels at different frequency bands are calculated, anoperation is carried out on the at least two calculated vibrationlevels, and the degree of slipperiness of the road surface is estimatedfrom computed value.
 5. A vehicle running state estimation methodcomprising: detecting a vibration level of a portion below a spring of arunning vehicle; and estimating the running state of the vehicle bydetermining a condition of a road surface on which the vehicle isrunning and a running state of each tire, wherein said determining isbased on the detected vibration level, and, wherein vibration levels ofat least two points of a portion below the spring with a buffer memberinterposed therebetween are detected to calculate a vibrationtransmission level of the portion below the spring between the twopoints at a predetermined frequency band; and the condition of the roadsurface is estimated from the calculated vibration transmission level.6. A vehicle running state estimation apparatus comprising: means ofdetecting a vibration level of a portion below a spring of a runningvehicle; means of calculating a vibration level at a predeterminedfrequency band by analyzing frequency of the detected vibration level;and road surface condition estimation means for estimating a conditionof the road surface on which the vehicle is running by comparing thecalculated vibration level with the master curve which is the vibrationlevel detected through running on a road having a predetermined roadsurface condition, wherein the running state of the vehicle is estimatedbased on the condition of the road surface from the road surfacecondition estimation means.
 7. The vehicle state estimation apparatusaccording to claim 6, wherein the master curve is prepared based on thevibration level detected through the running on the surface of a usualroad with dry asphalt pavement.
 8. A vehicle running state estimationapparatus comprising: means of detecting a vibration level of a portionbelow a spring of a running vehicle; and road surface conditionestimation means for estimating a degree of slipperiness of a roadsurface from a value obtained by carrying out an operation on at leasttwo vibration levels at different frequency bands by analyzing thefrequency of the detected vibration level, wherein the running state ofthe vehicle is estimated based on the degree of slipperiness of the roadsurface received from the road surface condition estimation means.
 9. Avehicle running state estimation apparatus for estimating a runningstate of a vehicle based on a condition of a road surface comprising:means of detecting vibration levels of at least two points on a portionbelow a spring of the running vehicle with a buffer member beinginterposed therebetween; means of calculating a vibration transmissionlevel at a predetermined frequency band between said at least twovibration detection points; and road surface condition estimation meansfor estimating a condition of the road surface on which the vehicle isrunning from the calculated vibration transmission level.
 10. A vehiclerunning state estimation apparatus comprising: means of detecting avibration level of a portion below a spring of a running vehicle; meansof calculating a vibration level at a predetermined frequency band byanalyzing frequency of the detected vibration level; and road surfacecondition estimation means for estimating a degree of slipperiness ofthe road surface on which the vehicle is running from the calculatedvibration level, wherein the running state of the vehicle is estimatedbased on the degree of slipperiness of the road surface received fromthe road surface condition estimation means, and wherein a road surfacefriction coefficient μ at a time of running the vehicle is estimatedbased on a relationship between a surface friction coefficient μobtained from braking distances of the vehicle under various roadconditions at different speeds and at least one of the calculatedvibration level at said predetermined frequency band and a calculatedvibration transmission level.
 11. A vehicle running state estimationapparatus comprising; means of detecting a vibration level of a portionbelow a spring of a running vehicle; means of calculating a vibrationlevel at a predetermined frequency band by analyzing frequency of thedetected vibration level; and road surface condition estimation meansfor estimating a degree of slipperiness of the road surface on which thevehicle is running from the calculated vibration level, wherein therunning state of the vehicle is estimated based on the degree ofslipperiness of the road surface received from the road surfacecondition estimation means, and wherein the frequency band is a bandincluding frequency of natural vibration of a tire tread land portion.12. A vehicle running state estimation apparatus comprising: means ofdetecting a vibration level of a portion below a spring of a runningvehicle; means of calculating a vibration level at a predeterminedfrequency band by analyzing frequency of the detected vibration level;and road surface condition estimation means for estimating a degree ofslipperiness of the road surface on which the vehicle is running fromthe calculated vibration level, wherein the running state of the vehicleis estimated based on the degree of slipperiness of the road surfacereceived from the road surface condition estimation means, and wherein athreshold value is set for the vibration level, and the surface of theroad is estimated to be in a low friction condition when the calculatedvibration level exceeds the threshold value.
 13. The vehicle runningstate estimation apparatus according to claim 12, wherein the thresholdvalue can be changed.
 14. A vehicle running state estimation apparatusfor estimating running state of a vehicle based on road surfaceconditions, the estimation apparatus comprising: means of detecting avibration level of a portion below a spring of a running vehicle; meansof computing waveform of time changes in the vibration level; and roadsurface condition estimation means for estimating a condition of a roadsurface on which the vehicle is running from the vibration level at apredetermined position of the waveform or for a predetermined timerange.
 15. The vehicle running state estimation apparatus according toclaim 14 further comprising means of calculating the vibration level ofat least one of a tire leading edge portion, tire ground contact portionand tire trailing edge portion of the waveform.
 16. The vehicle runningstate estimation apparatus according to claim 14 which further comprisesa vehicle speed detection means to estimate the condition of a roadsurface based on vehicle speed.
 17. The vehicle running state estimationapparatus of claim 14, further comprising: means of judging slipperinessof the road surface based on the condition of the road surface estimatedby the road surface condition estimation means; and warning means forgiving a warning when it is judged that the condition of the roadsurface is slippery.
 18. The vehicle running state estimation apparatusaccording to claim 17, further comprising: vehicle speed detection meansto change decision on the slipperiness of the road surface and warninglevel based on vehicle speed.
 19. The vehicle running state estimationapparatus according to claim 14, further comprising a transmitter fortransmitting output of the vibration detection means for calculating atime change in the vibration level or a vibration level at apredetermined frequency band.
 20. The vehicle running state estimationapparatus according to claim 14 further comprising a power generatingunit mounted on a tire wheel, wherein the power generating unitgenerates power by rolling of each tire and supplies power for at leastone of driving the vibration detection means and amplifying output ofthe vibration detection means.
 21. A vehicle control apparatuscomprising vehicle control means for controlling the running state of avehicle based on the condition of the road surface estimated by thevehicle running state estimation apparatus of claim
 14. 22. The vehiclecontrol apparatus according to claim 21 which comprises vehicle speeddetection means to control the running state of the vehicle based onvehicle speed.
 23. The vehicle control apparatus according to claim 21,wherein the vehicle control means controls locked state of each wheel.24. The vehicle control apparatus according to claim 21, wherein thevehicle control means controls attitude of the vehicle.
 25. The vehiclecontrol apparatus according to claim 21, wherein the vehicle controlmeans controls air pressure of each tire.
 26. The vehicle controlapparatus according to claim 21, wherein the vehicle control meanscontrols idling state of each wheel.
 27. The vehicle control apparatusaccording to claim 21, wherein the vehicle control means changesinter-vehicle distance set value of an automatic driving system.
 28. Atire wheel comprising: the vehicle running state estimation apparatusfor estimating a running state of the vehicle by detecting the vibrationlevel of the portion below the spring as set forth in claim 14, and apower generating unit for generating power by a rolling of each tire andsupplying power to the estimation apparatus.
 29. The tire wheelaccording to claim 28, wherein the vehicle running state estimationapparatus is mounted to the tire wheel.
 30. The tire wheel according toclaim 28, wherein the power generating unit comprises a rotor magnetizedand rotated by the rolling of each tire, a stator made from a highmagnetic permeability material and adjacent to the rotor and a powergenerating coil installed within a magnetic circuit including the rotorand the stator.
 31. The tire wheel according to claim 30, wherein thepower generating unit comprises means of accumulating electromotiveforce generated in the power generating coil.
 32. The tire wheelaccording to claim 30, wherein the rotor is turned by rotating anunbalance weight the gravity center of the rotary cone of which iseccentric to a rotary shaft by the rolling of each tire.
 33. The tirewheel according to claim 30, wherein an air stream generated by therolling of each tire is introduced into the power generating unit andthe rotor is turned by the introduced air stream.